I have a single polygon in a local projection system. I would like to convert that polygon into an image that can be used as an overlay on google maps. I understand that it may be better to use existing projects such as Mapnik, but I am still interested in the process of turning coordinates into pixels.

My scripts current flow is as follows:

Convert polygons to Google Spherical Mercator Projection.

Divide the coordinates by the map resolution (metres per pixel) for the zoom level in question.

Transform the coordinates of the polygon to be relative to the origin of the image.

Render the coordinates to an image file.

Will such a process result in a cartographically correct rendering of the data? Am I leaving anything out?